Genetics and Evolution - Evolution - Speciation

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Introduction

• Speciation is the process through which new species arise.
• It involves the formation of reproductive barriers between populations.
• Speciation is driven by genetic changes and natural selection.

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Reproductive Isolation

• Reproductive isolation prevents gene flow between populations.
• Examples of reproductive barriers:
  • Geographic barriers
  • Temporal isolation
  • Behavioral isolation
• These barriers can lead to speciation.

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Geographic Barriers

• Geographic barriers physically separate populations.
• Examples:
  • Mountains
  • Oceans
  • Deserts
• Isolated populations can accumulate genetic differences.

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Temporal Isolation

• Temporal isolation occurs when populations reproduce at different times.
• Examples:
  • Plants with different flowering seasons
  • Animals with different mating seasons
• Populations become reproductively isolated due to timing differences.

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Behavioral Isolation

• Behavioral isolation occurs when populations have different mating behaviors.
• Example:
  • Different courtship rituals in birds
• Populations do not recognize each other as potential mates.

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Genetic Changes

• Genetic changes play a crucial role in speciation.
• Mutations introduce new genetic variations.
• Genetic recombination and gene flow can also contribute to speciation.

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Natural Selection

• Natural selection acts on individuals with certain traits.
• Traits that increase reproductive success are favored.
• Over time, beneficial traits become more common in the population.

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Types of Speciation

• Allopatric speciation:
  • Populations become geographically isolated.
  • Genetic changes accumulate, leading to speciation.
• Sympatric speciation:
  • Speciation occurs within the same geographic area.
  • Reproductive barriers evolve between subpopulations.

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Allopatric Speciation

• Allopatric speciation occurs due to geographic isolation.
• Geographic barriers prevent gene flow between populations.
• Genetic changes accumulate independently in each population.
• Eventually, the populations become reproductively isolated.

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Sympatric Speciation

• Sympatric speciation occurs without geographic isolation.
• It involves the development of reproductive barriers within a population.
• Example:
  • Polyploidy in plants can lead to instant reproductive isolation.

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These are the first 10 slides for the lecture on “Genetics and Evolution- Evolution - Speciation”. 11. Reproductive Strategies

• Different reproductive strategies can lead to speciation.
• Example:
  • Insect-plant interactions:
    • Some insects are specific pollinators for certain plants.
    • This specialization can lead to reproductive isolation.

12. Genetic Drift

• Genetic drift can contribute to speciation.
• It is the random change in allele frequencies over time.
• Population bottlenecks and founder effects are examples of genetic drift.

13. Adaptive Radiation

• Adaptive radiation is the rapid diversification of a single ancestral species.
• It occurs when a population colonizes new environments with diverse ecological niches.
• Example:
  • Darwin’s finches in the Galapagos Islands.

14. Hybridization

• Hybridization can occur between different species.
• Sometimes, hybridization can lead to speciation.
• Example:
  • Eastern and Western meadowlark hybridizing and forming a distinct species.

15. Punctuated Equilibrium

• Punctuated equilibrium is a pattern of evolution that involves long periods of stasis followed by rapid bursts of change.
• It suggests that speciation can occur relatively quickly.
• Example:
  • Fossil records showing sudden appearance of new species.

16. Gradualism

• Gradualism is a pattern of evolution that suggests species evolve slowly and gradually over time.
• It involves small incremental changes in populations.
• Example:
  • Fossil records showing gradual changes in a species over millions of years.

17. Convergent Evolution

• Convergent evolution is the process whereby different species independently evolve similar traits.
• It can lead to the formation of analogous structures.
• Example:
  • Wings in birds and bats.

18. Divergent Evolution

• Divergent evolution is the process whereby related species evolve different traits.
• It can lead to the formation of homologous structures.
• Example:
  • Forelimbs of mammals.

19. Co-evolution

• Co-evolution occurs when two or more species reciprocally influence each other’s evolution.
• Example:
  • Pollination interactions between flowers and their pollinators.

20. Speciation and Biodiversity

• Speciation is a fundamental process in the generation of biodiversity.
• The formation of new species contributes to the diversity of life on Earth.
• Studying speciation can help us understand the origin and maintenance of biodiversity.

21. Modes of Speciation

• There are two main modes of speciation:
  • Gradual speciation: Occurs through a slow accumulation of genetic changes over time.
  • Rapid speciation: Occurs through sudden genetic changes leading to the formation of a new species.

22. Gradual Speciation

• Gradual speciation involves small, incremental changes in the gene pool over an extended period.
• It is often driven by natural selection and genetic drift.
• Example:
  • Darwin’s finches in the Galapagos Islands, where small beak changes led to the formation of different species.

23. Rapid Speciation

• Rapid speciation occurs when significant genetic changes happen in a short period.
• It can be triggered by events such as polyploidy or hybridization.
• Example:
  • The formation of the Hawaiian silversword plants through hybridization and adaptive radiation.

24. Allopatric Speciation - Geographic Isolation

• Allopatric speciation occurs when populations are physically separated by a geographic barrier.
• The isolated populations have limited or no gene flow.
• Example:
  • The formation of different species of cichlid fish in African rift lakes due to geographical barriers.

25. Allopatric Speciation - Genetic Changes

• Genetic changes in allopatric speciation occur independently in each isolated population.
• Mutations, genetic drift, and natural selection play significant roles in driving speciation.
• Accumulated genetic differences lead to reproductive isolation.

26. Sympatric Speciation - Reproductive Barriers

• Sympatric speciation occurs without geographic isolation.
• Reproductive barriers evolve within a single population, leading to reproductive isolation.
• Example:
  • Apple maggot flies that have evolved to use different host plants for egg-laying and breeding.

27. Sympatric Speciation - Polyploidy

• Polyploidy is a condition where an organism has multiple sets of chromosomes, usually due to errors in cell division.
• Polyploidy can lead to immediate reproductive isolation and the formation of a new species.
• Example:
  • Wheat species with different levels of polyploidy, such as tetraploid and hexaploid wheat.

28. Sympatric Speciation - Niche Differentiation

• Niche differentiation refers to the specialization of populations in different ecological niches within the same geographic area.
• This specialization can lead to reproductive isolation and the formation of distinct species.
• Example:
  • Darwin’s finches in the Galapagos Islands, with different beak sizes for feeding on various food sources.

29. Hybrid Zones

• Hybrid zones are regions where two different species come into contact and can interbreed.
• They provide opportunities for gene flow between species.
• Hybrid zones can play a significant role in speciation by providing genetic variation for natural selection.
• Example:
  • The hybrid zone between the European Quercus robur and the American Quercus rubra oak species.

30. Conclusion

• Speciation is a complex process driven by genetic changes and reproductive barriers.
• Allopatric and sympatric speciation are two main modes of speciation.
• Each mode involves different mechanisms and can occur through various factors.
• Understanding speciation helps explain the diversity of life on Earth.

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